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Beams of sound immerse you in music others can’t hear

From restaurant music that only certain tables can hear to flying emails, the ability to place sound exactly where you want it has all kinds of unusual uses

By Paul Marks

Hear your emails

(Image: Trevor Williams/Fiz-iks/Getty)

IF YOU’RE sick of wading through a clogged email inbox or scrolling through endless Twitter timelines, Jörg Müller has a more fun way of sifting through your messages&colon; sound.

In his audio-enabled “BoomRoom” at the Technical University of Berlin, Germany, emails and tweets fly around you like a flock of birds, each chirping a subtly different sound that identifies the sender. More urgent messages whizz directly over your head. Touch one and a computer reads it out.

Being able to direct sound in such a focused way has only recently become possible thanks to smarter audio processing algorithms, directional loudspeakers and gesture-recognition technology, says Müller. His flying email concept might still seem a bit far-fetched, but steering sound exactly where it is wanted is already catching on elsewhere in a number of different real-world applications. One day, it might even help create smart homes that can speak to their visually impaired owners.

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For example, Parametric Sound of San Diego, California, has developed a highly directional “hypersound” loudspeaker that makes audible sound ride on an inaudible ultrasound carrier wave. This allows a gamer to be immersed in stereo audio that only they can hear – and it was a gaming highlight of January’s Consumer Electronics Show in Las Vegas, Nevada.

Hypersound is also being trialled in branches of McDonald’s in Disneyland and North Euclid, California. “There’s often a TV on in McDonald’s but not everyone wants to listen to it. So you can decide whether you want the TV sound beamed to your table,” says Parametric Sound spokesman David Lowey. In toy shops, the Build-A-Bear chain is beaming instructions on how to build the toy to children using hypersound. “Car makers are looking at it too – so only the driver hears the GPS navigation instructions,” Lowey says.

Directed sound could be used in cars so that only the driver hears the GPS navigation instructions

Back in Berlin, the BoomRoom consists of a ring of 56 loudspeakers that allow sounds to be assigned stationary or mobile positions in the space around you (see diagram). An array of 16 gesture-recognising cameras allows you to control what those sounds do. A music track, for instance, could be assigned to an object in the room such as a vase. To play the track you simply pick up the vessel and “pour out” a track in mid air. Gestures such as moving your hands apart or bringing them together can alter qualities like volume, treble and bass. “The instruments exist in mid-air so you can do your own sound mixing,” says Müller, whose team is working alongside Sascha Spors of the University of Rostock, Germany.

The BoomRoom relies on a technique developed at the Delft University of Technology in the Netherlands called wave field synthesis (WFS). This constructs a 3D sound field by cancelling and reinforcing sound waves in much the same way as a hologram does with light waves. The trick is to use an algorithm that controls the speakers precisely and uses constructive and destructive interference of the sound waves to place sounds where they are wanted, moment by moment. “It’s actually easier to produce a 3D sound field than it is with light because audio frequencies are so much lower,” says Spors.

Timing so many loudspeakers at once is crucial and it has only just become possible because the computer power needed to run the algorithms has finally been developed, says Müller. The speakers aren’t special in any way&colon; all the WFS algorithms need to know is where each speaker is. “All the magic happens in software,” says Müller. The system will be presented at the annual computer human interaction conference in Toronto, Canada, in April.

For Müller, the standout application of this technology is as a future smart room for people who are blind or sight-impaired. If a blind person entered a room, the important objects inside could announce their location. Users could also leave messages for one another in mid-air to be read out by a computer.

Another aim is to assign sounds to items in a room to reduce the number of gadgets we need. A bowl of marbles, for instance, could become an answering machine&colon; the bowl could click when there are messages in it – and the user picks up a marble to hear a message. When they have heard it, pretending to pluck it out of the marble deletes the message.

To work in everyday life, the hope is that the flat panel actuators that act as loudspeakers by making glass and other flat surfaces vibrate will drop in price in coming years, making it cheap enough to fill houses with them. “We believe that in the future loudspeaker panels will be integrated in walls,” says Müller.

The technology could also be a boon to gamers. The BoomRoom was first used for an audio-based lightsaber game in which a blindfolded person had to react to the “zummm, zummm” of a digital adversary’s lightsaber, their voice or their breath on the back of their neck. It worked too well&colon; “They found it impressively immersive and fun to use. But some hit out quite frantically and we had to calm them down to stop them hitting the speakers,” says Müller.

Sound sculptor Bill Fontana of San Francisco, California – who once turned London’s Millennium Bridge into a “live musical instrument” playing in the hall of the nearby Tate Modern – describes the Berlin technology as having fantastic potential to push sound in novel directions. “There is a lot of uncharted territory with using sound in our living and architectural spaces. Culturally, we are acoustically illiterate in many ways and regard most sound as noise.”

This article appeared in print under the headline “Pure sound, direct to you”